The present invention is directed to luminescent materials, to methods of making such materials, and to methods of using such materials. More particularly, the present invention is directed to high brightness, yellow emitting triboluminescent phosphors, especially useful in low-pressure fluorescent lamps intended for general lighting purposes.
Yellow-emitting phosphors that are efficiently excited by 254 nm radiation are presently required as the dominant component in two-phosphor blends, for high-brightness, low-pressure fluorescent lamps see, H. F. Ivey, J. Opt. Soc. Amer., 53: 1175(1963) and W. Walters, Appl. Optics, 10. The material that is currently employed in the commercial products of this type of high brightness lamp is calcium fluoroapatite coactivated with Sb and Mn. One such commercial phosphor, GTE Sylvania Type 4381, available from the Chemical and Metallurgical Division, GTE Precision Materials Group, Towanda, PA 18848, was used as the reference material herein.
In the calcium fluoroapatite matrix, abbreviated herein CaFAP, the Mn emission occurs in the yellow spectral region, and peaks at about 575 nm. In view of the well known inability of Mn.sup.2+ to efficiently absorb 254 nm radiation in most host lattices, one must discover a suitable sensitizer, that can be relied upon to absorb the exciting radiation and then to transfer it to Mn.sup.2+. In the Type 4381 phosphor, the role of sensitizer is performed by Sb.sup.3+. Since, in turn, Sb.sup.3+ has a fairly broad emission with peak at 500 nm in the CaFAP matrix, and since the sensitization process does not completely quench the intrinsic emission of Sb.sup.3+, the phosphor in question does not exhibit a yellow emission, but a whitish emission, due to the combination of the emission bands from activator and sensitizer. See for example, H. F. Ivey, J. Opt. Soc. Amer., supra and W. Walters, Appl. Optics, supra.
In the two-component blend scheme the highest brightness of the resulting white field is obtained by combining a narrow-band yellow emission with peak at 575 nm, and a narrow-band blue emission with peak at about 445 nm. It is evident that CaFAP:Sb:Mn does not strictly fulfill the requirements expected of the yellow-emitting component of the two-phosphor blend, because of the additional band peaking at about 500 nm and contributed by Sb.sup.3+.